I believe that is the over-sized punching bag that Bob Wall bought Bruce Lee as a joke.
Bob Wall Interview | cityonfire.com | Asian Film Reviews | Movie News
Bob Wall: And so I went as a joke, made him a 300 pound bag. I don’t think there’s a bag bigger than that. And so I stuffed it and called Bruce up in Bel Air and he had a Porshe, and I said “Hey Bruce, why don’t you come on down, I made you a man-sized bag” and he came and Joe and a bunch of our students all hid, I got on the phone, pretending to be on the phone, and I said “Yeah Bruce, go ahead and throw it in the back, its in there hanging up” and so he walked in and the expression on his face would have been great to have on film, and we all fell over when he saw the size of bag…